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Gamma radiation induced immobilization of several polydimethylsilane liquid stationary phases for use in packed-column gas chromatographic separations has been studied. Extraction tests show that moderate doses of gamma radiation (80-140 kGy) are sufficient to produce significant (90%) immobilization of most polydimethylsilanes onto Chromosorb supports, although a molecular mass effect is seen. Thermal stability also increases significantly with radiation dose, suggesting higher temperature use with smaller volatility losses. Infrared spectra confirm the continued presence of the stationary phase on the support after thermal stability tests and after exhaustive in-column washing. The column chromatographic behavior of the immobilized phases is equal to or better than that of the unirradiated phases, except for higher doses (300 kGy) of gamma-radiation. Columns prepared from gamma-immobilized polydimethylsilane have been used successfully in analyses where column contamination from high boiling materials requires frequent column recuperation.

In liquid-liquid extraction performed by monosegmented flow analysis (MSFA), the aqueous sample is introduced between two air bubbles and flows, under restricted dispersion, through a glass extraction tube where the analyte is retained, usually at pH higher than 8. The retained analyte is removed to a small volume of an organic phase containing a ligand which is introduced after the second air bubble. In this work, the effect of the organic phase composition on the extraction of Cu(II), Zn(II) and Cd(II) in MSFA systems was investigated by changing the ethanol content (0.1-4% v/v) in toluene, chloroform and carbon tetrachloride. The extracting efficiency of the organic phases containing ethanol was evaluated by using dithizone (DT), 1-2-pyridylazo-2 naphthol (PAN) and sodium diethyldithiocarbamate (DDTC) as ligands for the metals. The MSFA extraction system was improved by introducing a new syringe-based device for organic phase delivery. The presence of ethanol in the organic phase shows a remarkable (up to ten times) effect on the extraction efficiency of the flow system when DT is employed. Its presence is mandatory if DDTC is used, as it accounts for ligand solubility in the organic phase. The extraction efficiency also increases with the pH of the aqueous phase as a consequence of higher ionisation of the glass silanols, where the analytes are adsorbed before extraction. The system has been evaluated for determination of Zn(II) in drugs showing a mean R.S.D. of 2.2% and mean relative accuracy of 4.4%, when compared with atomic absorption spectrometry results. Typical sample frequency, sample and organic phase consumption are 30 samples per hour, 200 and 100 mul, respectively.

Peroxidase was extracted from a natural source (turnip) and irradiated with 60Co (0.1 kGy). It was then used in the construction of biosensors for hydrogen peroxide determination, in order to study the effect of the gamma irradiation on the performance of the biosensors. The biosensors were constructed using two immobilization procedures: cross-linking with glutaraldehyde and covalent binding through carbodiimide. The biosensor prepared using covalent binding through carbodiimide showed a higher sensitivity for H2O2. A good enhancement in stability and sensitivity was obtained for the biosensors from irradiated material, when compared to biosensors prepared with non-irradiated enzyme. However, the initial linear response range (1.0 to 10.0 mmol dm-3) and response time (0.5 s) were equal with or without irradiation.

An automated system to perform titration and standard addition in monosegemented flow analysis by employing the simultaneous multiple injection is described. The system was controlled by aPC-AT-386 microcomputer through a home-made parallel interface, employing a diode array spectrophotometer as detector. Software was written in QuickBasic 4.5 to control the system and for data acquisition. A three-way solenoid valve was used in conjunction with a proportional injector to add the titrant solution or the standard solution to the sample, to carry out titration or standard addition, respectively. Only one standard solution was used in each procedure and different quantities of titrant or standard were added to the sample by controlling the time interval in which the solenoid valve was switched on. Titration and standard addition curves similar to those of the manual methods were obtained in both cases, since the sample dispersion was very low due to the air bubbles of the monosegment. The titration system was evaluated through the determination of Fe(II) with a KMnO4 standard solution in pharmaceutical preparations. The standard addition process was assessed by determining Cr(VI) in natural waters and domestic wastewater using the diphenylcarbazide method. The results obtained in both methodologies did not differ significantly from the reference methods at a 95% confidence level.

An automated system to perform liquid-liquid extraction in monosegmented flow analysis is described. The system is controlled by a microcomputer that can track the localization of the aqueous monosegmented sample in the manifold. Optical switches are employed to sense the gas-liquid interface of the air bubbles that define the monosegment. The logical level changes, generated by the switches, are flagged by the computer through a home-made interface that also contains the analogue-to-digital converter for signal acquisition. The sequence of operations, necessary for a single extraction or for concentration of the analyte in the organic phase, is triggered by these logical transitions. The system was evaluated for extraction of Cd(II), Cu(II) and Zn(II) and concentration of Cd(II) from aqueous solutions at pH 9.9 (NH(3)/NH(4)Cl buffer) into chloroform containing PAN (1-(2-pyridylazo)-2-naphthol) . The results show a mean repeatability of 3% (rsd) for a 2.0 mg l(-1) Cd(II) solution and a linear increase of the concentration factor for a 0.5mg l(-1) Cd(II) solution observed for up to nine extraction cycles.